Segmented sleep may be the natural pattern
Several lines of evidence suggest that this archaic sleep pattern may, in fact, be the natural sleep pattern—the one most in tune with our inherent circadian rhythms and the natural environment. In the early 1990s, Thomas A. Wehr, MD, then a sleep researcher at the NIMH, and his colleagues reported that when 8 healthy men had their light/dark schedules shifted from their customary 16 hours of light, 8 hours of dark to one in which they were exposed to natural and artificial light for 10 hours each day and confined to a dark room for 14 hours each night (durations of light and dark similar to the natural durations of day and night in winter) a sleep pattern similar to that of the preindustrial era developed.2,3 They slept in 2 bouts of about 4 hours each separated by 1 to 3 hours of quiet wakefulness. Subjects usually woke from their first bout of sleep during a period of rapid eye movement (REM) sleep, when dreaming is most likely. The second bout of sleep was usually lighter than the first, with less stage-4 (deep) and more REM sleep.4 Thus, when freed from the time constraints on night imposed by modern work schedules and artificial illumination, subjects reverted to the segmented sleep of earlier times.
Also suggesting that interrupted or segmented sleep comes to us naturally, many animals that are active during the day—including chimpanzees, chipmunks, and giraffes—sleep at night in 2 distinct bouts separated by several hours.4-6 In fact, Wehr points out, modern humans may be unique among animals in the extent to which their sleep is consolidated.
Wehr, now a Scientist Emeritus at the NIMH, thinks that our current sleep pattern, in which we fall asleep rapidly and expect to sleep (and often do) for an uninterrupted 7 or 8 hours, may be an artifact of both chronic sleep deprivation and artificial light. When the subjects of his experiments shifted from the 16-hour "days" and 8-hour "nights" customary for them (and for everyone else in developed countries) and which depend on artificial light, to the "natural winter" conditions of his experiment, they slept at first for 11 hours and then started sleeping for an average of 8.9 hours, compared with 7.2 hours under ordinary conditions.3
These and other data7 suggest that our current schedules do not allow us the sleep that we require. Wehr also observed that when given 14 hours of darkness, it took subjects at bed rest about 2 hours to fall asleep, compared with the 15 minutes under usual conditions.4 He speculates that under usu- al conditions, we may fall asleep so quickly because we are chronically sleep-deprived. Natural sleep, Wehr suggests, particularly during relatively long periods of darkness, is characterized by a long sleep latency and "interspersed with periods of wakefulness."4
The discoveries of Ekirch and Wehr raise the possibility that segmented sleep is "normal" and as such they hold significant implications for both the understanding of sleep and the treatment of insomnia. But sleep specialists are, for the most part, unaware of these findings and have not yet incorporated them in clinical practice. Part of the reason lies with the fact that these discoveries have not been widely disseminated. Ekirch's book received a good number of deservedly positive reviews, but it is, after all, history and is not at the top of most reading lists. While Wehr's sleep research is well known to sleep specialists, the thrust of his work has been on uncovering the mechanisms governing sleep. His discovery of segmented sleep was an unexpected, incidental finding from a study examining the influence of photoperiod on sleep and melatonin(Drug information on melatonin).2